An abrasive particle compact is a polycrystalline mass of abrasive particles such as diamond and/or cubic boron nitride bonded together to form an integral, tough, high-strength mass. Such components can be bonded together in particle-to-particle self-bonded relationship, by means of a bonding medium disposed between the particles, or by combinations thereof. For examples, see U.S. Pat. Nos. 3,136,615; 3,141,746; and 3,233,988. A supported abrasive particle compact herein termed a composite compact, is an abrasive particle compact which is bonded to a substrate material, such as cemented tungsten carbide. Compacts of this type are described, for example, in U.S. Pat. Nos. 3,743,489, 3,745,623, and 3,767,371. The bond to the support can be formed either during or subsequent to the formation of the abrasive particle compact.
Composite compacts have found special utility as cutting elements in drill bits. These compacts can be attached directly to the drill crown of drill bits by a variety of techniques. U.S. Pat. No. 4,156,329 proposes to furnace braze a pretinned metal-coated compact to recesses formed in the crown. U.S. Pat. No. 4,186,628 proposes to attach the compact cutters to the crown by placing the compacts in a mold, filling the crown portion of the mold with powder, and running a low temperature infiltration braze into the mold to form the crown containing the compacts embedded therein. U.S. Pat. No. 4,098,362 proposes drill bits in the manner of the latter proposal wherein the cutter are placed at a rank angle of between -10.degree. and -25.degree..
Alternatively, composite compacts can be affixed to an elongated stud or substrate which stud then is attached to the drill crown. The stud provides greater attachment area to the drill crown. It also provides more support for the abrasive particle compact thereby increasing its impact resistance. Composite compacts have been attached to studs in both a right cylinder configuration as depicted in U.S. Pat. No. 4,200,159, and in an angled configuration, as shown, for example, in U.S. Pat. No. 4,265,324.
Although the benefits of attaching a composite compact to a stud or substrate are apparent, problems have been encountered in achieving the actual attachment. In particular, it has been noted that composite compacts in which the abrasive portion is self-bonded and metal infiltrated such as described in U.S. Pat. No. 3,745,623 and available commercially under the trademarks Compax and Syndite are susceptible to thermal damage if exposed to temperatures in excess of about 700.degree. C. (As used herein self-bonded means that the abrasive particles are directly bonded one to another.) This damage is thought to result from a differential in the thermal expansion rate of the abrasive and metal phases. At elevated temperatures there is also a risk of degradation to the particles themselves as by graphitization or oxidation. This type of degradation is thought to be of concern for all types of abrasive particle compacts. Accordingly, braze alloys with liquidus temperatures of less than 700.degree. C. were utilized initially for attachment of composite compacts to studs or substrates. Unfortunately, such low temperature braze alloys found only limited applicability in the marketplace due to their characteristically low bond strengths.
A major breakthrough in the attachment of composite compacts to substrates was made by Knemeyer in U.S. Pat. Nos. 4,225,322 and 4,319,707. The Knemeyer process permits the use of high temperature braze alloys for attaching a composite compact to a substate. Such high temperature braze alloys, in turn, provide significantly greater bond strengths. While the Knemeyer method and apparatus permit the use of high temperature braze alloys, difficulty has arisen in the selection of a suitable one. For example, Anaconda 773 filler metal, initially proposed in the Knemeyer patents, is now thought to be undesirably reactive with the carbide pieces being joined.
Complicating the braze material selection is the fact that the braze must not only be suitable for joining a composite compact support to a substrate, but it must also be capable of withstanding subsequent manufacturing and operating conditions. For example, a common manufacturing method includes first tinning the brazed implement and then furnace brazing the pre-tinned implement to recesses cut in a drill crown in the manner of U.S. Pat. No. 4,156,329 (cited above). Braze joints made using prior braze materials have had difficulty in withstanding such tinning and furnace brazing operations. Bond strength during these operations is especially critical since the bond is believed to be under tensile strain following the initial brazing procedure. Finally, to function in typical drilling environments it is thought that the braze joint must be designed to be capable of withstanding temperatures of up to about 400.degree. C. in an oxidizing atmosphere while being subjected to continuous impact loading as would be the case if heterogeneous formations were encountered.